This study aims to expand the work done on the previous (subproject 220) protocol by administering 2-CdA to patients with documented chronic progressive multiple sclerosis with a subcutaneous injection given for five days each month for six months in a double-blind, placebo-controlled, crossover design. MRI will be followed at baseline, and at 6, 12, 18 and 25 months after initiation of therapy. Standardized neurological rating assessments will be applied.